Voice over internet protocol (“VoIP”) communication systems allow the user of a device, such as a personal computer, to make calls across a computer network such as the Internet. These systems are beneficial to the user as they are often of significantly lower cost than fixed line or mobile networks. This may particularly be the case for long distance calls. To use VoIP, the user must install and execute client software on their device. The client software provides the VoIP connections as well as other functions such as registration and authentication. In addition to voice communication, the client may also provide video calling and instant messaging (“IM”).
One type of VoIP communication system uses a peer-to-peer (“P2P”) topology built on proprietary protocols. To access the peer-to-peer system, the user must execute P2P client software provided by a P2P software provider on their PC, and register with the P2P system. When the user registers with the P2P system the client software is provided with a digital certificate from a server. Once the client software has been provided with the certificate communication can subsequently be set up and routed between users of the P2P system without the further use of a server. In particular, the users can establish their own communication routes through the P2P system based on exchange of one or more digital certificates (or user identity certificates, “UIC”) to acquire access to the P2P system. The exchange of the digital certificates between users provides proof of the user's identities and that they are suitably authorised and authenticated in the P2P system. Therefore, the presentation of digital certificates provides trust in the identity of the user. It is therefore a characteristic of peer-to-peer communication that the communication is not routed using a server but directly from end-user to end-user. Further details on such a P2P system are disclosed in WO 2005/009019.
VoIP communication systems therefore have a valuable resource in that each user has a contact list of other VoIP system users (contacts). This provides a level of trust between the users. Currently, however, these contact lists are only used for initiating communication events between the user and contact or contacts (e.g. VoIP calls, IM chat, video calls, file transfers, etc.)